within acceptable limits are needed. Among the many possible solutions, electrochemical CO 2 reduction (ECR) offers a potentially sustainable approach not only for depressing CO 2 concentration but also converting it into fuels and commodity chemicals. [2] Unfortunately, the CO chemical bond in CO 2 (≈806 kJ mol −1 ) is thermodynamically very stable and its conversion is an uphill energy process with a high activation barrier. Moreover, during electrochemical reduction of CO 2 , the hydrogen evolution reaction (HER) inevitably occurs as a competing reaction, which is a major stumbling block for CO 2 reduction especially in aqueous electrolytes. [3] From these scenarios, robust catalysts that can selectively reduce CO 2 in lieu of protons at high turnover frequency (TOF) and faradaic efficiency (FE) for CO 2 reduction are desired.Since Hori's pioneering study on electroreduction of CO 2 in the 1980s, [4] Cu, [5] Au, [6] Ag, [7] Zn, [8] Sn, [9] and Bi [10] among others, have been widely investigated for electrocatalysis of CO 2 reduction, due to their promising capability to convert CO 2 into valuable chemicals and fuels while the HER is largely suppressed. Earth-abundant first-row transition metals such as Fe, Co, and Ni, however, are highly active for HER and also easily Electrochemical reduction of carbon dioxide (CO 2 ) to fuels and value-added industrial chemicals is a promising strategy for keeping a healthy balance between energy supply and net carbon emissions. Here, the facile transformation of residual Ni particle catalysts in carbon nanotubes into thermally stable single Ni atoms with a possible NiN 3 moiety is reported, surrounded with a porous N-doped carbon sheath through a one-step nanoconfined pyrolysis strategy. These structural changes are confirmed by X-ray absorption fine structure analysis and density functional theory (DFT) calculations. The dispersed Ni single atoms facilitate highly efficient electrocatalytic CO 2 reduction at low overpotentials to yield CO, providing a CO faradaic efficiency exceeding 90%, turnover frequency approaching 12 000 h −1 , and metal mass activity reaching about 10 600 mA mg −1 , outperforming current state-of-the-art single atom catalysts for CO 2 reduction to CO. DFT calculations suggest that the Ni@N 3 (pyrrolic) site favors *COOH formation with lower free energy than Ni@N 4 , in addition to exothermic CO desorption, hence enhancing electrocatalytic CO 2 conversion. This finding provides a simple, scalable, and promising route for the preparation of low-cost, abundant, and highly active single atom catalysts, benefiting future practical CO 2 electrolysis.

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A Co atom enhances the HER activity of monolayer MoS2 whereas a Ni atom exhibits the opposite effect on the same basal site.

Hydrated niobium oxides are used as strong solid acids with a wide variety of catalytic applications, yet the correlations between structure and acidity remain unclear. New insights into the structural features giving rise to Lewis and Brønsted acid sites are presently achieved. It appears that Lewis acid sites can arise from lower coordinate NbO and in some cases NbO sites, which are due to the formation of oxygen vacancies in thin and flexible NbO systems. Such structural flexibility of Nb-O systems is particularly pronounced in high surface area nanostructured materials, including few-layer to monolayer or mesoporous NbO·nHO synthesized in the presence of stabilizers. Bulk materials on the other hand only possess a few acid sites due to lower surface areas and structural rigidity: small numbers of Brønsted acid sites on HNbO arise from a protonic structure due to the water content, whereas no acid sites are detected for anhydrous crystalline H-NbO.

Photocatalysis shows a great potential for N2 fixation to NH3 under mild conditions, which intrigues increasing research attention in recent decades. To this end, the design of efficient photocatalysts is the key. Herein, we report the synthesis of single atom Ru decorated TiO2 nanosheets rich in oxygen vacancies. Single Ru sites greatly promoted photoreduction of aqueous N2 to NH3, affording an NH3 formation rate of 56.3 μg/h/gcat. We found that isolated Ru atoms likely weakened the hydrogen evolution, promoted absorption of N2, and also improved the charge carrier separation, which led to enhanced N2 photofixation.